Various types of vapor degreasing and vapor drying devices and processes are known in the art for use in the removal of contaminants from process parts and components. Specifically, degreasers include machines designed to clean grease and foreign matter from mechanical parts and like items usually metallic by exposing them to vaporized or liquid solvent solutions confined in a tank or vessel. Generally, the solvents used in degreasers include polyhalogenated hydrocarbons that remove fat or oil from parts and related industrial processes. Unlike degreasers, however, the use of superheat to remove such contaminants requires a delicate balance of system components to establish and maintain a vapor zone within which much of the cleaning or drying is accomplished. Few, if any, systems exist which optimize heat balance, heat load, and throughput of components in the manner achieved by the present invention. However, of the systems which are at least known in principle, the following points are considered relevant.
Generally, vapor cleaners and dryers use various means for boiling a volume of solvent which results in heated vapors used to clean and/or dry the parts inserted into the vapor zone. Technical disclosures of such systems may specify use of quartz tanks, electric heaters, and other components so that boiling solvent is generated directly below a parts load. The parts may be separated from the boiling solvent (boil sump) by a drip tray. A common problem of these and similar systems relates to the re-flashing of water that has been removed from the parts as it gravitates toward the bottom of the system. This results in system inefficiencies and recontamination problems.
Known vapor dryers are also susceptible to vapor zone collapse under heavy parts loading. This "work shock" occurs when a large mass and/or surface area of process parts at a sub-cooled temperature rapidly condenses all available solvent vapor in the vapor zone, allowing surrounding air to rush into the dryer to fill the void. This condition is undesirable, as it allows for potential contamination of the parts, produces uneven heating and vapor rinsing as the vapor blanket is reestablished from the bottom up, and adds unnecessary delays to process cycle times while the vapor zone recovers.
Known vapor drying systems have also accomplished parts drying in an upper cooling zone above the air-vapor interface line in the condensing region. At the end of the rinsing cycle, process parts in these types of Systems have a thin film of liquid solvent, referred to as "dragout", remaining on them as they leave the vapor zone. In this upper cooling zone, the hot parts will immediately release this liquid to the relatively cooler air in the upper cooling zone via evaporation, allowing for the complete drying of parts before they are withdrawn from the system. This method is undesirable, however, as the solvent vapors are then scavenged by the system ventilation exhaust, or lost forever as fugitive vapor emissions out of the top of the equipment.
These and other problems are overcome by use of the superheated vapor drying techniques and system described below.